Authenticate with Firebase

Integrate GitHub authentication into your app by following the
developer's documentation. Use the web application flow, and set up a
custom URL scheme in your app to handle the OAuth 2.0 callback from GitHub.
At the end of the GitHub sign-in flow, you will receive an OAuth 2.0 access
token.

Next steps

After a user signs in for the first time, a new user account is created and
linked to the credentials—that is, the user name and password, phone
number, or auth provider information—the user signed in with. This new
account is stored as part of your Firebase project, and can be used to identify
a user across every app in your project, regardless of how the user signs in.

In your apps, you can get the user's basic profile information from the
FIRUser object. See Manage Users.

In your Firebase Realtime Database and Cloud Storage
Security Rules, you can
get the signed-in user's unique user ID from the auth variable,
and use it to control what data a user can access.